Re: [SAGE] number of eggs in a basket

[Brad Knowles <brad@stop.mail-abuse.org>]

At 10:57 AM -0500 2005-01-07, Xev Gittler wrote:

>  David Parter wrote:
>
>>  We believe very strongly in only one service per server.
>
>  That works on a small scale. However, it can be extraordinarily wasteful
>  in the large scale.

	It works well on a large scale, too.  AOL was living proof, at 
least as of the time I was there.  Pournelle's Law was "At least one 
CPU per person", and AOL adapted that to be "At least N+M systems per 
service".


	AOL also set up multiple separate "pods", each of which could 
potentially operate as a totally separate completely contained AOL 
system, or at least all the necessary front-end bits that are 
required to handle the client connections, which then connect via 
load-balanced/fault-tolerant cluster systems for the back-end 
services.

	Put a couple of pods in Europe, and that's all that's needed to 
handle up to a million-plus customers, talking to the AOL back-end 
systems in Reston and Springfield, Virginia.  Put a couple of pods in 
Japan, too.

>                      Given the size of even the smallest machines, a
>  single service can use a minuscule amount of the CPU.

	Depends on the service, and how your systems are designed.  If 
the CPU is always 100% idle, that may not be a problem -- so long as 
you're keeping the network I/O pipes filled.

>                                                         While this won't
>  make much of a difference on one machine, 1000 machines each running at
>  a trivial utilization level, is an expensive waste of resources,
>  regardless of how cheap each piece of hardware is.

	Maybe.  It might be "cheap at any price", due to the extreme 
imbalance between CPU speeds and I/O speed, and the way off-the-shelf 
systems are designed.

	YMMV.

>  Clearly, you need to balance service requirements vs. criticality vs.
>  stability, etc,

	As far as that goes, I agree.

>                  but managing services, and running multiple ones on a
>  machine, perhaps migrating them as necessary is a more effective use
>  of resources. I don't want to suggest that you should do this on huge,
>  expensive machines, but there is a sweet spot for this hardware, and
>  it is more capacity than most services require.

	The key is to do a proper cost/benefits analysis, and do what is 
right for you.  What is right for AOL or Google may not be right for 
Mom & Pop Ltd, and vice-versa.

-- 
Brad Knowles, <brad@stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.